1. Field of the Invention
The present invention relates to an intermediate transferrer to which a toner image formed in accordance with an electrostatic latent image on a photoconductor is to be transferred from the photoconductor as well as a transfer device and an image forming apparatus each including the intermediate transferrer.
2. Description of Related Art
In a general electrophotographic image forming apparatus, an electrostatic latent image is formed on a photoconductor, a toner image according to the electrostatic latent image is transferred to a recording medium such as normal paper, and the toner image is fixed onto the recording medium, whereby an image is formed on the recording medium. An apparatus including an intermediate transferrer is known as such an image forming apparatus as described above. In this image forming apparatus, a toner image is transferred from the photoconductor to the intermediate transferrer, and is then transferred from the intermediate transferrer to the recording medium.
Such transfer of the toner image from the photoconductor to the intermediate transferrer and then from the intermediate transferrer to the recording medium is performed by forming an appropriate electric field that promotes toner movement. From the perspective of securing the quality of a final image, electrical characteristics of the intermediate transferrer are important, and thus have been studied up to now.
For example, Japanese Patent Application Laid-Open No. 2009-265343 describes a multilayer elastic belt serving as an intermediate transferrer and including a substrate layer, an elastic layer formed thereon, and a surface layer formed on the elastic layer. Then, at 23° C. and 55% RH, the common logarithm value of the volume resistivity of a belt including the elastic layer and the surface layer is larger than that of a belt including the substrate layer.
For example, Japanese Patent Application Laid-Open No. 2007-292887 describes a transfer belt serving as an intermediate transferrer and including a base layer, an intermediate layer formed thereon, and a surface layer formed on the intermediate layer. Then, the surface resistivity of the base layer is larger than that of the intermediate layer.
The electrical characteristics of the intermediate transferrer change depending on environments surrounding the intermediate transferrer. For example, under a low-temperature low-humidity environment, as illustrated in FIG. 1A, electric charges are more likely to remain in intermediate transferrer 10. If electric charges injected from transfer roller 15 remain in intermediate transferrer 10, particularly, elastic layer 11, a discharge phenomenon may occur between intermediate transferrer 10 and photoconductor 20, on a more downstream side than a nip section (pre-nip section) formed by intermediate transferrer 10 and photoconductor 20 (for example, in a main nip section), a transfer failure may occur, and image noise may occur.
Meanwhile, under a high-temperature high-humidity environment, as illustrated in FIG. 1B, electric charges are likely to diffuse in intermediate transferrer 10. If the diffusion of the electric charges is promoted, an unnecessary electric field is generated in the pre-nip section, with the result that image disturbance may occur due to excessive current.
As described above, there is still a room for study to suppress a transfer failure due to the electrical characteristics of the intermediate transferrer at the time of an environmental fluctuation.